"Also, some more options to add to your decision process, there is a seller in Japan with a lot of new-old-stock NOS on the big auction site now.
Check out some of his RB and RZ gear. His auction site handle is, sanpoucamera"

There were some concerns last year over Mamiya NOS lenses--both RB+RZ--that showed their age with fungus issues. One busy HK eBay dealer, the now-defunct "wkcrs," sold tons of lenses that made it to resellers who spread the problem. Not sure "sanpou" is among them but it might be wise to check their refund policies.